1 ) The value of ∆H (O-H) is 109 k cal / mol . The formation of 1 mole of water in gaseous state from H(g) and O(g) is accompanied by : -

1 ) The value of ∆H (O-H) is  109  k cal / mol . The formation of 1 mole of water in gaseous state from H(g) and O(g) is accompanied by : -

Solution : -

H2 + O2  ------->  2 (OH)

So , 2 (109) = 218 .

So , water is liquid  , So energy is released .

So  ∆H = - 218 K cal  ,  Answer .

 

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2 ) The enthalpies of combustion of carbon and carbon monoxide are  - 390 K J / mol  and  - 278 K J / mol  respectively . The enthalpy of formation of carbon mono oxide ?

Solution : -

Combustion of carbon : -

C + O2  ---------->  CO2  ,  ∆H = - 390   . . . . . . . . . . . eq. 1

Combustion of carbon mono oxide : -

CO + (1/2) O2  ---------->  CO2  ,  ∆H = - 278   . . . . . . . . . . . eq. 2

So  ,  eq. 1 – eq. 2 : -

C + O2 - CO - (1/2) O2  ---------->  CO2 – CO2  ,  ∆H = - 390 – ( - 278 ) .

C - (1/2) O2  ---------->  CO  ,  ∆H = - 112  K J / mol  ,  Answer .

 

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3 ) Latent heat of vaporization of a liquid at 500 k and 1 atm pressure is 10.0 k cal / mol . What will be the change in internal energy ∆E of 3 mol of liquid at same temperature ?

Solution : -

3 H2O (L)  ------------->  3 H2O (g) .

So  ,  ∆n = 3 .

So , ∆E = ∆H - ∆nRT .

∆E = ( 3 x 10 ) – 3 x 500 x 0.002  = 27 k cal  ,  Answer .

 

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4 ) The bond dissociation energies of H2 , Cl2 and HCl are 104 , 58 and 103 k cal  respectively . The enthalpy of formation of HCl gas will be ?

Solution : -

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